1. Field of the Invention
The invention relates to audio wideband beam steering or forming from multiple sources, and in particular to beam forming by passive group delay.
2. Related Art
Loudspeaker systems have been implemented as arrays of loudspeakers, or drivers; either stacked and aligned vertically, aligned horizontally, or in two dimensions. The drivers in such configurations may be of the same type, such as tweeters, midrange speakers, or wideband speakers. The drivers may also be connected to cross-over networks, or filters to generate sound in particular frequency ranges.
One problem with loudspeaker systems arranged in an array is that the sound generated by multiple drivers does not create a consistent sound field or pattern. This inconsistency in the sound field or pattern distorts the sound and impairs the listening experience of the listener.
One solution to the problem is to utilize a digital delay to effectively move the apparent sound from a driver in the array by introducing time delay creating a more consistent coverage. Another solution involves physically placing each driver appropriately in space to create a more consistent sound field. In either solution, the drivers are generally arranged in an arc or spherical shape either through time delay or, physically placed to form an arc or sphere, to provide a desired coverage.
A constant beam width transducer (CBT) is a type of sound transducer designed to provide a listening area with a sound beam that projects at a constant angle. The source of sound projects substantially at an angle and forms the listening area within the space defined by the angle sides. One design goal is for CBT's to project the sound at the same frequency response and volume at any point along any arc of points equidistant to the source. A CBT's beamwidth is defined as an angle. Studies of CBTs show that a curved line array or spherical array will have a constant beam width of approximately 66% of the total physical arc. The CBT also requires that the elements in the array be ‘shaded.’ That is, the drivers in the center are loudest, and the speakers on either side are attenuated more and more along the arc towards the ends of the array. The time delay or physical curving creates the coverage pattern and the shading smoothes the on- and off-axis response. By using time delay, the arc or sphere can be created from a straight line or flat 2-D array, respectively. This is often preferable for esthetic and space reasons. However providing a separate amp channel and associated digital time delay for each device can be expensive.
It would be desirable to provide an arc coverage pattern using a straight or flat speaker array without the need for expensive digital time delay circuitry.